The histone genes of the sea urchin provide one of the best systems for the study of gene regulation in eukaryotic organisms. There are several hundred copies of each histone gene in the genome. The genes are organized into a repeating unit of 6-7 kb, which contains the genes for the five histones interspersed with five spacer regions. The availability of cloned histone DNA recombinants provides suitable nucleic acid hybridization probes to investigate both the nature of the genes and the presence of complementary transcripts. Our objectives are twofold: a) To learn more about the organization of the histone genes -the extent of length heterogeneity and where it exists and the identity and organization of the genes coding for the sequence variants of Hl, H2A, and H2B histones. b) To study the regulation of histone synthesis during development, including the basis of control of transcription of these genes. The first set of studies will employ the techniques of restriction enzyme mapping, Southern transfer hybridization, electron microscopic visualization of DNA heteroduplexes, and recombinant DNA techniques. The second objective will be pursued by the use of cell-free translational systems and RNA-DNA hybridization to assay for content, rate of synthesis, and turnover times of each histone mRNA. An in vitro system will be used to assay the factors involved in the control of gene transcription. Our results should provide significant information on the maintenance, organization, evolution, and regulation of the histone genes.